1. Field of the Invention
The present invention relates to a lubricating oil additive comprising an alkaline earth metal salt of a sulfurized monoalkylcatechol as a main component, and more particularly to a lubricating oil additive, particularly a lubricating oil additive for an internal combustion engine which is excellent in anti-oxidant, friction-reducing and anti-abrasive properties and comprises a lubricating oil additive comprising an alkaline earth metal salt of a sulfurized monoalkylcatechol as a main component, and a process for producing the same. The present invention also relates to a lubricating oil composition comprising said lubricating oil additive.
2. Prior Art
In recent years, a remarkable lowering in fuel consumption and an increase in output have been made on internal combustion engines. This requires lubricating oils to have a capability of lowering the abrasion and oxidation stability and detergency at high temperature.
The function of monoalkylcatechols as an antioxidant and an abrasion inhibitor of lubricating oils and as a deposit inhibitor of diesel engines is described in U.S. Pat. No. 4,643,838. Further, U.S. Pat. No. 4,729,848 describes that metal salts of monoalkyl catechol dithiophosphoric acids are useful as an anti-wear agent of lubricating oils for gasoline and diesel engines. The monoalkylcatechols, however, have a problem in the anti-oxidant property at high temperature. Further, since the metal salts of monoalkyl catechol dithiophosphoric acids contain phosphorus poisonous to exhaust gas purification catalysts, the use thereof should be limited by more severe regulation of exhaust gas in the future.
U.S. Pat. No. 4,221,673 reports that a lubricating oil additive having an excellent rust preventive property can be produced by adding 10 to 50% by weight of an alkyldihydroxybenzene in the production of a sulfurized or non-sulfurized phenate. This patent, however, reports that the viscosity of the formed overbased sulfurized phenate increases with increasing the amount of addition of nonylcatechol and, when the amount of the nonylcatechol is 100%, the lubricating oil additive solidifies by the addition of calcium hydroxide. In the production of the nonsulfurized phenate, the product is a physical mixture of an alkylphenol with an alkyldihydroxybenzene, while in the production of the sulfurized phenate, the product is a compound comprising an alkylphenol and an alkyldihydroxybenzene bonded to said alkylphenol through sulfur crosslinking. Thus this patent does not take into consideration the use of the alkylcatechol or sulfurized alkylcatechol as such.
U.S. Pat. No. 4,115,287 describes a lubricating oil composition comprising a sulfurized dihydroxy benzene having an alkyl group of at least 7 carbon atoms and also reports that the composition has an excellent rust preventive property and excellent stability against oxidation. The compounds disclosed in this patent, however, have a problem in the friction-reducing properties, anti-abrasive properties and colour stability.